This continuation-in-part describes polyester resin films that incorporate vapor corrosion inhibitors and meet the recently approved compostable plastics standard of ASTM, D5338 dated Apr. 10, 1999. Films are also described that will meet the proposed CEN draft standards made public Dec. 8, 1998, as PREN 13427.
The present invention relates generally to an improved, more environmental friendly resinous product particularly useful in packaging and/or packing applications. The product incorporates the features of biodegradability together with the incorporation of a vapor phase corrosion inhibitor for protection of metallic surfaces positioned in proximity to the material, such as for example, when held or contained within an enclosure prepared from the product as a film or shroud. Plastic films and packing materials formed of raw materials which are biodegradable are commercially available, and because of their more environmental friendly properties, they are becoming more and more in demand. For example, plastic resin films have a wide variety of uses, including forming enclosures such as shipping sacks for creating a protective environment for metallic articles. Additionally, resinous products may be prepared from other base materials, with such articles having found specific application as bulk packing dividers or filler objects useful in a variety of packaging applications. While conventional films or objects fabricated from polyolefin resins have found wide application for packaging purposes, the need for resin products which are biodegradable and compostable is both recognized and for a variety of applications, is becoming a requirement. Because of their different physical properties, however, these products prepared from biodegradable materials possess some disadvantageous characteristics or properties which may be overcome through utilization of the features of the present invention.
Biodegradable plastic films or objects have certain physical and mechanical properties which differ from those of the conventional and well-known polyolefin films such as polyethylene and polypropylene. For example, the commercially available biodegradable films have significantly higher breathability and moisture attraction and permeability. Because of these physical properties, biodegradable plastic films typically offer less protection to metallic articles than is available from the more traditional polyolefin films. However, this disadvantage may be overcome when the biodegradable plastic resin film is combined with a particulate vapor phase corrosion inhibitor dispersed within and through the film or coated on the surface of the film. The selected vapor phase corrosion inhibitors used in connection with the present invention are highly compatible with biodegradable resins and films, and offer significant protection to metallic articles within an enclosure. In particular, those films comprising a film forming resin selected from the group consisting of a polylactic acid homopolymer, a polycaprolactone polymer or other suitable polyesters including those prepared with adipic acid, succinic acid, and butanediol. Films comprising these resins in either their pure or blended form possess the property of biodegradability along with higher permeability and higher breathability when compared to those same properties exhibited by conventional polyolefin films.
In the formation of enclosures or shrouds for metallic articles, certain applications find the higher permeability and breathability to be an advantage. Such applications include enclosures for high humidity environments to avoid "greenhouse" effects. To offset the greater permeability and accessibility of the enclosure to corrosive atmospheres rich in water vapor, salt air, carbon dioxide, sulfur dioxide, hydrogen sulfide, or other gases which pose a threat to the surfaces of metallic objects, a vapor phase corrosion inhibitor in films of the type selected for this invention will provide significant protection for metallic articles, as well as other advantages.
The selected vapor phase and contact corrosion inhibitors which have been found highly effective for use in connection with the present invention are amine salts, ammonium benzoate, alkali molybdates, alkali nitrites, alkali dibasic acid salts, tall oil imidazolines, and triazole compounds. These materials have been found to have highly effective corrosion inhibiting properties when combined with or coated on films in accordance with the present invention. The corrosion inhibitors are preferably prepared and available in particulate form with particles being of a preferred size range. For most film applications, the corrosion inhibitors found most useful have a maximum particle size range less than about 50 microns, with a size of between about 20 and 30 microns being preferred.
When a film substrate has served its intended purpose and is to be discarded, it is becoming more and more important that the composition from which the film is formed be biodegradable and compostable. Indeed, certain legislation has been proposed which would ban the disposal of bags fabricated from non-biodegradable plastic film from compost heaps or piles. In this connection, standards have been adopted for classifying film bags as compostable and biodegradable, with this standard normally providing that no more than 10% of the film's original weight can remain on a 3/8th-inch screen following 12 weeks of exposure to a compost medium. Resin films prepared from a polymer resin selected from the group consisting of polylactic acid homopolymer, polyesters of butanediol, adipic acid, succinic acid, and small amounts of terephthalic acid and/or polycaprolactone meet these standards and can be blended with starch derivatives for some applications as a means of reducing the cost or enhancing biodegradability. The biodegradable properties and characteristics of these films are not adversely affected when blended with one or more of the particulate corrosion inhibitors as set forth hereinabove.
Turning now to the biodegradable film substrates, a lactic acid homopolymer is commercially available from Cargill, Inc. of Minnetonka, Minn. under the trade designation "Ecopla 4200-D", with this homopolymer being useful in the production of biodegradable films. Additionally, materials available from Mitsui Chemicals Inc. of Japan under the trade designation "Lacea" may be used. A biodegradable film forming resin available from BASF of Parsippany, N.J. under the trade designation "Ecoflex" is useful for forming film products. Polyester polymers prepared from polycaprolactone are commercially available from Union Carbide under the trade designations "TONE", and "EASTAR" is commercially available from Eastman Chemical. "Bionolle", a polyester available commercially from Showa Denko of Japan, is particularly useful as a film, a foam, or a non-woven sheet that can be coated or extruded in contact with corrosion inhibiting chemicals. Each of these resins may be compounded with the selected vapor and contact corrosion inhibitor chemicals or formulations to produce films capable of enhanced corrosion protection to the surfaces of packaged metallic articles. At the same time, when these films have served their useful purpose, they may be discarded as biodegradable materials to be received in conventional composting fields.
It is recognized that biodegradable films are more environmentally friendly, since the degradation of the film renders it more acceptable for use in situations where composting occurs. In accordance with the present invention, biodegradable films may be utilized in applications when the films are combined with the corrosion inhibitors of the type selected for use in connection with the present invention.